Communication procedures within mobile radio communications network can involve amounts of data of various signals and recent discussion within 3GPP (3rd Generation Partnership Project) documentation in particular has focused on the transmission of small amounts of data by way of SDT features and services.
Many Machine Type Communication (MTC) applications send or receive small amounts of data. 3GPP Services and Systems Aspects (SA1) Working Group has already identified SDT as one possibly attractive feature for MTC. According to Technical Specification document TS22.368, s7.2.5, the MTC Feature ‘Small Data Transmission’ is intended for use with MTC Devices that send or receive small amounts of data and the size of many of the instances of data exchange is on the order of 1 k (1024) octets.
Also, 3GPP Services and System Aspects (SA2) Working Group has considered Small Data Transmission optimisation as part of the MTCe-SDDTE (Small Data and Device Triggering Enhancements) Work Item, as discussed in particular as section 5.1 of the Technical Report TR23.887. One key issue identified is the desire to ‘Efficient Small Data transmission’ and the following functional requirement for Small Data transmission has been determined, i.e. systems should support transmissions of small amounts of data efficiently with minimal network impact such as signalling overhead, network resources and delay for reallocation.
3GPP SA2 Working Group has already agreed several suggested solutions for such efficient transmissions are known from TR23.887.
Also, during its last meeting (SA2#98, July 2013) SA2 recommended ‘Standalone Small Data Service with T5/Tsp and generic NAS (Non-Access Stratum) transport’ for standardisation and identify a protocol for SDT to carry small data units of various users of that small data service was agreed and which spans between service accesses points in the User Equipment UE device and the SCS/AS (Service Capability Server/Application Server). As discussed further below with reference to FIG. 1, any service data exchange between the UE and Application Server (AS) is intended to go through the MTC-IWF (Machine Type Communication-Interworking Function) and the SCS. The small data transfer can be provided as confirmed or unconfirmed delivery service.
An Illustration known from TR23.887, of uplink Small Data Transmission (SDT) through control plane channel on T5 and Tsp interfaces is also discussed further below with reference to FIG. 2.
However, such suggested protocol details are not fully defined and so are incomplete.
Although an existing protocol could be adopted for the SDT protocol, there are many new and specific requirements that would make simple adoption of current protocols inappropriate. One such specific issue is how to control the use of SDT at the both sides, the UE and the network. Indeed an Editor's Note in the TR23.887 confirms that the manner of ensuring that the application correctly uses the Service Request procedure and does not abuse this ‘Small Data’ NAS procedure is an open issue. However the MME's (Mobile Management Entity) ability to release the connection provides a control point.
Yet further in its Liaison Statement (LS) answer to (R2-133033) SA2, RAN 2 Working Group has suggested that it is essential to ensure that only traffic matching small data feature characteristics can use SDT solution since the use with other traffic patterns would result in deterioration in capacity and performance.
It is also noted that, while with the normal data transmission there is an initial PDP/PDN (Packet Data Protocol/Packet Data Networks) connection establishment that could be rejected, with a SDT service there is no PDP/PDN connection establishment that occurs before sending the SDT.